The present invention relates to a semiconductor manufacturing apparatus for manufacturing semiconductor elements such as Integrated Circuits (ICs) from wafers such as silicon wafers.
One of the processes for manufacturing semiconductor elements such as ICs is a chemical vapor deposition (hereinafter abbreviated as "CVD") process, or diffusion process, for producing various types of thin films on the surface of silicon wafers.
A conventional semiconductor manufacturing apparatus is described in the following, using a vertical CVD apparatus having a vertical furnace as an example.
To handle and transport wafers, a predetermined number (e.g. 25 pcs.) of wafers are generally loaded and transported by a wafer cassette. A conventional semiconductor manufacturing apparatus is provided with a cassette stocker, which accommodates in turn the wafer cassettes for one batch of wafers. The wafers are removed from the wafer cassettes for processing.
The following describes a conventional vertical CVD apparatus with reference to FIG. 14.
In a cubicle 1, a reaction furnace 2 is provided, and a boat elevator 3 is furnished under the reaction furnace 2. A wafer transfer system 4 is placed parallel to the boat elevator 3, and a cassette stocker 5 is provided near the wafer transfer system 4.
The boat elevator 3 inserts and retrieves the boat 6 loaded with horizontally stacked wafers into and out of the reaction furnace 2. The boat 6 is placed in a boat receiver (not shown), which is supported by a guide rod 7. Further, the boat receiver is connected to a screw rod 8 and a motor (not shown) so that the boat 6 is moved up and down through rotation of the screw rod 8 by the motor.
The cassette stocker 5 delivers and receives the wafer cassettes 10 used to load or store wafers 9. In the present example, the cassette stocker 5 can accommodate wafer cassettes in two columns having five shelves, and the cassette stocker 5 can be moved horizontally with respect to the columns of the cassette stocker 5.
The wafer transfer system 4 comprises a lifting block 12 supported by a guide rod 11; a screw rod 14 which is rotated by a motor 13 and engaged with the lifting block 12 by a screw; and a wafer handling head 15 mounted on the lifting block 12. By moving the wafer handling head 15 and the associated lifting block 12 up and down, the wafer transfer system 4 transfers wafers 9 from the wafer cassette 10 situated in the cassette stocker 5 to the boat 6 or transfers wafers 9 from the boat 6 to the wafer cassette 10 situated in the cassette stocker 5.
The following describes the flow of wafer processing, referring to FIG. 15.
The wafer cassette 10 containing wafers 9 is moved and stored in a box which is filled with antioxidant gas while awaiting film forming processing. The wafer cassette 10 is taken out of the box when film processing is to begin. When taken out, the wafer cassette 10 is automatically or manually moved into the vertical CVD apparatus and situated in the cassette stocker 5.
The wafers 9 of the wafer cassette 10 situated in the cassette stocker 5 are transferred to the boat 6 by the wafer transfer system 4. When a predetermined number of the wafers 9 have been transferred to the boat 6, the boat elevator 3 places the boat 6 into the reaction furnace 2.
The interior of the reaction furnace 2 is heated to a preset temperature by heating means 20. The air in the furnace is discharged by a discharging means 18. Further, reaction gas 16 for forming film is introduced into the furnace by a reaction gas introducing means 17.
The reaction gas is introduced at a ratio of preset quantity into the reaction furnace 2 during the processing of the wafers 9 and the gas is discharged by the discharging means 18 after processing.
The reaction gas introduced into the reaction furnace 2 reacts and decomposes due to heat in the furnace. The reaction gas is then deposited on the surface of the wafers 9, and thin film as desired is formed.
When the film has completely formed, the boat 6 is removed by the boat elevator 3, and the wafer transfer system 4 transfers the wafers 9 from the boat 6 to an empty wafer cassette 10 on the cassette stocker 5.
Then, the same procedure is repeated, and films are formed sequentially on each of the wafers 9 in each of the wafer cassettes 10 which are accommodated in the cassette stocker 10. The wafer cassette 10 containing the processed wafers is then removed from the cubicle 1 after processing has been completed.
As described above, a conventional semiconductor manufacturing apparatus is provided with only one set of cassette stockers and can accommodate the wafer cassettes for only one batch of wafers. As a result, the wafer cassettes must be removed from the semiconductor manufacturing apparatus as soon as the processing of the wafers has been completed in order to empty the cassette stocker and subsequently move the next batch of wafer cassettes into the cassette stocker. Accordingly, wafer processing by the reaction furnace must cease while the wafer cassettes loaded with the processed wafers are replaced by the wafer cassettes loaded with the unprocessed wafers.
By the present invention, it is possible to increase wafer processing efficiency because the processing of wafers is not stopped even when the wafer cassettes, loaded with the processed wafers, are being replaced by the wafer cassettes loaded with the unprocessed wafers.
Further, natural oxidation of the wafers during the manufacturing process may negatively impact the quality of the product. The present invention can prevent the undesirable natural oxidation of wafers during the manufacturing process.